For preoperative analgesic regime, pregabalin 50mg are given the night before operation. Same analgesic regime is used on the day before operation. For intraoperative regime, standardized intraarticular local anaesthetic infiltration is used. For postoperative analgesic regime, PCA using morphine is used. In addition to PCA using morphine, standardized analgesic regime is used -- regular pregabalin 50mg nocte, paracetmal 1g QID, Celebrex 200mg BD will be given for 5 days.